Fin field effect transistor (finFET) designs require a different number of fins for different devices. For example, logic devices may need multiple fins together to function as one transistor for high drive current. In contrast, static random access memory (SRAM) may need only one fin per transistor to increase SRAM density.
For a same type of finFET transistor (e.g., an n-channel FET or nFET), the same epitaxial process is used to grow source/drain epitaxy. For logic transistors, it is desirable to have merged epitaxy. For SRAM, however, merged epitaxy is detrimental.
Using different fin pitches (tight fin pitch for merged epitaxy, and relaxed fin pitch for un-merged epitaxy) can enable merged epitaxy and un-merged epitaxy. However, relaxed fin pitch comes with the drawback of reduced transistor density.
Therefore, there is a need for forming finFET devices with merged source/drain epitaxy and un-merged source/drain epitaxy without different fin pitches.